1. Field of the Invention
The present invention relates to a hand-off processing apparatus and method for telecommunication system in which a transmission data is channel-coded and matched through a transmission rate matching algorithm, and more particularly, to a hand-off processing apparatus and method for telecommunication system in which a mobile terminal and two base stations transmit and receive two different transmission signals produced from a single communication signal in a soft hand-off processing, to thereby enhancing a communication quality and efficiency.
2. Description of the Background Art
Generally, a hand-off occurs frequently in a mobile communication system which consists of base stations and a mobile terminal As one of method for processing the hand-off, a soft hand-off processing method is widely employed.
A conventional mobile communication system using the soft hand-off method will now be described with reference to the accompanying drawings.
FIG. 1 is a block diagram of a CDMA (code division multiple access) diversity combining receiver of a base station in an up-link telecommunication system in which a data is transmitted from a mobile terminal to a base station in accordance with a conventional art.
The diversity technique refers to a receiving method for combining or converting receiving signals of various field strengths or various signal/noise ratios to obtain a single signal output to thereby reduce effect of a fading (in a wireless communication, when a radio wave is received through plural paths, the signals received through different paths interfere each other due to atmosphere refractivity change and obstacles, causing a change in an attenuation degree according to time change which leads to generation of distortion of ghost to the received signal).
As shown in FIG. 1, a CDMA diversity combining receiver of the base station includes a first and a second analog receivers 11 and 21 for receiving an analog radio frequency signal from a mobile terminal through antennas ANT1 and ANT2, converts the received radio frequency signal to an intermediate frequency signal, and amplifying and outputting the intermediate frequency signal; a first and a second searching units 12 and 22 for searching a signal transmitted from the mobile terminal among signals received through the first and the second analog receivers 11 and 21; a base station controller 31 for controlling rake receivers 13, 14, 23 and 24 to be described; a plurality of rake receivers 13, 14, 23 and 24 for transmitting a signal determined by the base station controller 31; a diversity combiner 32 for combining the signals transmitted from the plurality of rake receivers 13, 14, 23 and 24 to obtain a diversity and generating a signal; and a decoder 33 for decoding the combined signal and transmitting the decoded signal to a master switching center (MSC).
The operation of the CDMA diversity combining receiver of the conventional art constructed as described above will now be explained with reference to the accompanying drawings.
The two antennas ANT1 and ANT2 receive independently an analog frequency signal transmitted from a mobile terminal, respectively. Then, the first and the second analog receivers 11 and 21 receives the analog radio frequency (RF) signal, converts it to an intermediate frequency (IF) signal, amplifies the intermediate frequency signal and transmits it to the first and the second searching units 12 and 22 and to the plurality of rake receivers 13,14, 23 and 24.
Then, the first and the second searching units 12 and 22 searches a pilot signal (a synchronous signal transmitted to obtain a subcarrier indicating signal difference by a receiver in a wireless communication system) transmitted from the mobile terminal and computes a signal-to-interference ratio of the pilot signal. Then, the base station controller 31 discriminates which mobile terminal has transmitted the signal by using the computed value and informs the rake receivers 13, 14, 23 and 24 of the discrimination result.
Thereafter, in order to obtain a diversity, the diversity combiner 32 combines signals outputted from the plurality of rake receivers 13, 14, 23 and 24. The combined signal is subjected to decoding by the decoder 33 and transmitted to the master switching center.
FIG. 2 is a diagram showing a relationship between a mobile terminal communication with two base stations and the master switching center in a hand-off in accordance with the conventional art.
In the case that the mobile terminal 10A moves from a zone 20A of a base station ‘A’ 20A-1 to a zone 20B of a base station ‘B’ 20B-1, when the mobile terminal 10A enters the handoff region between the two base stations 20A-1 and 20B-1, hand-off occurs (the previous communication channel is switched to a communication channel of a new zone to go on to make a communication in a different quality).
In the hand-off region, the mobile terminal 10B of which a hand-off mode has been set transmits and receives a signal to and from the master switching center 100 through the base station ‘A’ 20A-1 and the base station ‘B’ 20B-1 simultaneously.
In this manner, during the soft hand-off operation in accordance with the conventional art, the mobile terminal improves a reliability of a signal by using the diversity method combining the signals transmitted from the several base stations by means of the rake receiver. That is, the mobile terminal 10B transmits and receives the same signal to and from the base stations ‘A’ and ‘B’.
However, the soft hand-off method of the conventional art has problems of signal interference (when a radio wave is received, various other radio waves are absorbed to interfere the original radio wave), fading of a signal and echoing of a signal (when a radio wave is received through more than two paths, the same signal repeatedly appears as the radio wave reaches at different time point due to the path difference, causing that a receiving signal is distorted or a sound quality is deteriorated.
The standard groups of the next generation mobile communication system such as 3GPP adopts a turbo coding as a standard of the mobile communication. The turbo coding refers to a method in which one signal is coded in a various methods and the generated coded signal is multiplied by a gain, and then the resulted signal is transmitted from a mobile terminal to a base station or from a base station to a mobile terminal, simultaneously.